1. Field of the Invention
The present invention relates to a slider device and a measuring instrument.
2. Description of Related Art
Conventionally, there has been a well-known slider device (see, for example, Reference 1: Japanese Laid-open Patent Publication No. 2002-299893, Reference 2: Japanese Laid-open Patent Publication No. 2003-172350, Reference 3: Japanese Laid-open Patent Publication No. H09-166137, and Reference 4: Japanese Laid-open Patent Publication No. 2003-311574).
FIG. 7 shows a conventional slider device based on the conventional technology.
A slider device 900 includes a longitudinally extended base 910 having a flat upper surface, a running head 920 running back and forth along a longitudinal direction of the base 910, a guide mechanism 930 for guiding a running direction of the running head 920, and a driving unit (not shown) for driving the running head 920.
The guide mechanism 930 includes two rails 931, 932 laid in parallel to each other on the upper surface of the base 910 and sliders 933, 934 provided over and sliding on the rails 931, 932. The sliders 933, 934 are attached to a bottom surface of the running head 920, and the running direction is guided by sliding those sliders 933, 934 along the rails 931, 932.
The driving unit includes a rack (not shown) provided between the rails 931, 932 in parallel to the rails 931, 932, a pinion (not shown) engaging with the rack, a motor (not shown) for driving to rotate the pinion (not shown).
The motor is fixed on the running head 920, and a rotor of the motor is connected to the pinion.
A tooth surface of the rack is provided on one side surface of the rack (a surface facing either one of the rails), and a direction of rotation axis of the pinion is perpendicular to an upper surface of the base 910.
In this configuration, when the motor rotates for driving, the pinion is rotated. Then, the pinion moves along the rack because of engagement with the rack. The running head 920 runs with the motor as the pinion moves. A direction of the running head 920 is guided along the direction of the rails 931, 932 as the running head 920 slides along the rails 931, 932.
The base 910 and the running head 920 were conventionally made of the same materials. For instance, the running head 920 and the base 910 were made of low thermal expansion materials which thermally deform little.
However, the running head 920 is desired to run at a higher speed in recent years. In order to achieve the object, it is necessary to make the running head 920 with light materials. However, when the running head 920 is made of light materials, the problem may arise that the running head 920 and the base 910 have different thermal expansion rates in response to a temperature change since the different materials are used for the running head 920 and the base 910.
Specifically, if thermal expansion of the running head 920 and that of the base 910 are different in the lateral direction, a force acting in the orthogonal direction to the rails 931, 932 is loaded to the rails 931, 932 and thus stress is generated in the rails 931, 932 and the sliders 933, 934, thereby the problem may arise that durability and geometric accuracy of the guide mechanism 930 (the rails and the sliders) are reduced. Then, another problem will also arise that running accuracy of the running head 920 becomes lower.